In recent years, solar cells directly converting solar energy into electrical energy have been increasingly expected as next-generation energy sources particularly from the viewpoint of global environmental issues. Though there are various types of solar cells such as those made of a compound semiconductor or an organic material, those made of crystalline silicon are currently mainstream.
The solar cells are classified into those having a structure (double-sided electrode structure) in which an electrode is placed on each of a light-receiving surface on which sunlight is incident and a back surface opposite to the light-receiving surface and those having a structure (back electrode structure) in which an electrode is placed only on a back surface. A solar cell with a back electrode structure is advantageous in that the amount of incident sunlight can be increased because no electrode is present on a light-receiving surface.
For example, Patent Literature 1 describes a solar cell with a back electrode structure. According to the solar cell described in Patent Literature 1, an in junction and an ip junction are placed on the back surface of a semiconductor substrate, an n-side electrode is placed on the in junction, and a p-side electrode is placed on the ip junction. In the solar cell, sunlight is incident on a light-receiving surface of the semiconductor substrate and therefore carriers are generated in the semiconductor substrate. The carriers are extracted outside through the p-side electrode and the n-side electrode.